Forging with fusible coating



United States Patent FORGING WITH FUSIBLE COATING Douglas Wilson Hall, Tynemouth, Northumberland, and George Oswald Eccles, Barrowford, England, assignors to Rolls-Royce Limited, Derby, England, a corporation of Great Britain N Drawing. Application July 27, 1954, Serial No. 446,171

Claims priority, application Great Britain August 7, 1953 4 Claims. (Cl. 29424) This invention relates to improvements in the hot forging of metals and more particularly to the preparation of a billet for hot forging, extrusion, rolling, pressing, die-stamping and the like.

In the manufacture of many kinds of metallic parts, especially :those of complex contour, the reduction or avoidance of machining to final shape is desirable. Forging, for example, by pressure between shaped dies, saves costly machining, but in some cases and for some purposes forging must be carried out at exceedingly high temperatures and, as a result, elaborate procedures are necessary to prevent oxidation of the finished surface. Atmospheres of inert gas are ditficult to apply in a forgeshop or foundry. Electro-plating with corrosion-resistant metal is time-consuming and costly and not always possible.

According to the present invention a metal billet is prepared for hot forging by applying to its surface to be shaped by the die a suspension in a liquid lacquer of finelydivided particles of an inorganic non-metallic compound insoluble in the lacquer and capable of existing in a fused state without decomposition at temperatures at which the hot forging is to be carried out. Thereupon the liquid of the lacquer is caused to dry off as, for example, by allowing it to evaporate, by heating the metal billet to a temperature suificien-t to drive off the liquid in the form of vapor, .or by burning it off thus depositing upon the surface of the billet a dry coating of said finely-divided particles. Finally, the metal billet is heated to the temperature at which it is to be hot-forged, thus causing the finely-divided particles on the surface of the metal to fuse together and form in contact with said surface a continuous protective film consisting of the said inorganic non-metallic compound. The term billet includes cast ingots, partly machined ingots, partly forged blanks or billets which may additionally be partly machined.

The lacquer may be any liquid lacquer which can be caused to dry off at temperatures below forging temperatures, such as a liquid solution or suspension of lacquer containing silicones and resins, for example of the melamine and epoxy types. The lacquer serves to bind the particles of the coating after driving off of the liquid and prior to heating up of the part to the temperature at which fusion occurs.

The inorganic non-metallic compound may be any com pound or mixture of compounds, natural or synthetic, which is insoluble or substantially insoluble in the lacquer, which is capable of being finely ground, which fuses at a temperature below that at which the hot forging is to be carried out, and which does not decompose or volatilize within the range of forging temperatures. Among the many compounds suitable for the purpose are various kinds of glass and ceramic materials. By way of example compounds which have been found suitable for use in connection with the hot-forging of blades for internal combustion turbine engines made of a titanium alloy or of a nickel-chromium-cobalt base alloy fall within the following:

The potash may be replaced wholly or in part by sodium carbonate. One preferred compound is as follows:

Percent Sand (Silica)--- 50.5 Red Lead (Pb304) 30.3

Potash (Potassium Carbonate Hydrated) 17.50

Potassium Nitrate 1.03 Arsenic Oxid 0.30

Borax 0.37

Variations of this composition may be made to raise or lower the fusion temperatures. For instance, a greater proportion of red lead may be used .to provide a lower fusion point.

The suspension may be made by grinding or ball-milling the material to such a particle size that when the suspension is applied it gives an even coating of the required thickness. The material used is that which passes through a mesh sieve but most of it may be finer.

The proportion of the ground material to the lacquer will depend upon the method of application. If the method is dipping a suspension consisting of one part of the ground material to three parts of the lacquer is suitable. If the material is to be applied by spraying a larger proportion of lacquer may be necessary.

It may be desirable to roughen the surface of the metal by wet or dry blasting or etching to facilitate the application of the coat and to promote its adhesion.

When the coat has been applied the lacquer liquid is dried off. This may be eifeoted by drying it off by the application of moderate heat. The coat should be dry before the part is .put into the furnace to be heated to the forging temperature.

While the range of temperatures within which metal may advantageously be hot forged is known or can be determined for each :of the known alloys, and therefore need not be specifically recited herein, an example of an application of this invention is in the hot forging of engineering parts made of nickel-chromium-cobalt alloys which contain a hardening element and are capable of being hardened by solution heat-treatment and ageing. Such alloys are commonly used for the rotor blades of internal combustion turbine engines. For proper shaping, this alloy must be hot-forged at temperatures of 1100 to 1200" C. (about 2000 to 2200 F.). At these highly elevated temperatures there is a pronounced tendency to superficial oxidation. If, prior to heating the metal billet to such a temperature, its surface is spread or coated with a liquid suspension as above described, :and the liquid is dried off at temperatures of, say, C., a dry coating of finely-divided particles is formed upon the surface. As the metal billet is heated towards 'll00 -C., the particles which comprise this coating fuse together on the surface and form a thin continuous protective film which ensures freedom from deleterious oxidation.

The part is then ready for forging. In the case of a turbine blade the part may be transferred to a forging die and during the forging operation the film will act as lubricant by preventing contact between the hot metal and the die. To afford adequate protection, only a very 7 p 3 rt-hinfilm is necessary and this can readily be removed afterwards by a light blasting operation which is simple and inexpensive. A thin, even coating prevents fouling of the dies in recesses and assists in obtaining a good smooth surface finish to the forging.

By the aforesaid means of preparing the metal billet for hot-forging, the same may be hot-forged .to finished size and contour, or to a size approximating finished size thereby obviating or'reducing complex machining and post-forging treatment other than removal of the protective film.

What is claimed is:

1. Method of preparing a metal billet for hot-forging comprising applying to a surface of said billet a suspension in lacquer of finely-divided particles of an inorganic non-metallic compound insoluble in said lacquer and capable of existing in fused state Without decomposition at forging temperatures, said lacquer containing a resin selected from the group consisting of silicone, mel- 'amine and epoxy resins; causing the lacquer .to harden so as to form upon said surface a continuous coating adherent to said metal consisting of a matrix of hardened resin containing said finely-divided particles; and hea-ting 'sa-id billet to forging temperature whereby the continuous coating of hardened resin is vaporized and replaced by a continuous coating adherent to said metal consisting of said particles of inorganic non-metallic compound fused together.

2. The method described in claim 1, wherein the resin is of the silicone type. x

3. The method described in claim 1, wherein the resin is of the melamine type.

4. The method described in claim 1, wherein the resin is of the epoxy type.

Marencik et al Jan. 11, 1949 

1. METHOD OF PREPARING A METAL BILLET FOR HOT-FORGING COMPRISING APPLYING TO A SURFACE OF SAID BILLET A SUSPENSION IN LACQUER OF FINELY-DIVIDED PARTICLES OF AN INORGANIC NON-METALLIC COMPOUND INSOLUBLE IN SAID LACQUER AND CAPABLE OF EXISTING IN FUSED STATE WITHOUT DECOMPOSITION AT FORGING TEMPERATURES, SAID LACQUER CONTAINING A RESIN SELECTED FROM THE GROUP CONSISTING OF SILICONE, MELAMINE AND EPOXY RESINS; CAUSING THE LACQUER TO HARDEN SO AS TO FORM UPON SAID SURFACE A CONTINUOUS COATING ADHERENT TO SAID METAL CONSISTING OF A MATRIX OF HARDENED RESIN CONTAINING SAID FINELY-DIVIDED PARTICLES; AND HEATING SAID BILLET TO FORGING TEMPERATURE WHEREBY THE CONTINUOUS COATING OF HARDENED RESIN IS VAPORIZED AND REPLACED BY A CONTINUOUS COATING ADHERENT TO SAID METAL CONSISTING OF SAID PARTICLES OF INORGANIC NON-METALLIC COMPOUND FUSED TOGETHER. 